Drive train for a motor vehicle

ABSTRACT

The invention concerns a drive train for a motor vehicle, which includes a coupling device ( 202 ) between a drive unit ( 232 ) and a transmission for moment transfer between the drive unit and the transmission, whereby the coupling device shows at least one coupling arrangement ( 204, 206 ) that can be activated by means of a pressure medium, for operation under the influence of an operating medium, and the transmission can be activated through the use of a pressure medium by means of a dedicated actuator ( 234 ), whereby, on the basis of a shared pump arrangement ( 209 ) that is or can be driven by the drive unit, i) the pressure medium can be provided for activation of the coupling arrangement, and ii) the operating medium can be conducted to the coupling device for the purpose of operating under the influence of the operating medium, and iii) the pressure medium can be provided for activation of the transmission, and whereby the pump arrangement includes at least one pump ( 209 ), which can be controlled or adjusted with regard to output pressure and/or with regard to output flow rate.

[0001] The invention concerns a drive train for a motor vehicle, which includes a coupling device between a drive unit and a transmission, whereby the coupling device shows at least one coupling arrangement which can be activated by means of a pressure medium, and whereby, in said coupling arrangement, the pressure medium is provided by means of a pump arrangement.

[0002] Coupling systems of this type are known, for example, from DE 100 56 954 A1 and DE 101 02 874 A1, and reference to the disclosed content thereof is expressly made in the description of the invention which appears below.

[0003] The coupling system is especially configured as a wet clutch double coupling system with two multiple disk clutch coupling arrangements, which can be activated in a hydraulic manner by means of slave cylinders integrated into the coupling device. Double coupling systems of this type are known, for example, from DE 100 04 179 A1.

[0004] Wet clutch double coupling systems, for the activation of the multiple disk clutch couplings, require a low flow rate of the pressure medium under high pressure; for cooling the friction pads and/or disks, they require a comparatively high flow rate of the operating medium, under comparatively low pressure. By comparison with conventional solutions that include a pump that is mechanically driven by the drive unit and that constantly provides a flow rate or output pressure corresponding to the rotational frequency of the drive unit at any given moment, the technique of using an independently adjusted pump arrangement for each flow rate is known, for example, from DE 100 56 954 A1 and DE 101 02 874 A1. In the case of pumps that are driven by an electrical motor, however, it has been shown that, with drive units characterized by especially high performance ratings and/or especially high rotational frequencies, the requirement of the coupling device for cooling oil can be so high that the use of an electrical motor to drive an electrical motor pump to cool the coupling device becomes inconvenient, as a result of the excessively large amount of room required for a pump of the desired performance rating. For energy-related reasons, however, returning to the conventional solution, which involves a pump that is permanently driven by the drive unit, cannot be envisioned. It is known from prior art that, even in the case of a pump that is permanently driven by the drive unit, it is possible to provide a means of controlling and/or adjusting the output pressure and/or the output flow rate of the pump, without requiring too great a degree of mechanical and control-related effort and expense.

[0005] The proposed invention is also based on the consideration that, in the case of a transmission that can be activated in a hydraulic manner, in order to save the need for a special pump dedicated to the transmission activation, it is also advantageous to provide the pressure medium for the activation of the transmission by means of the pump arrangement that is in charge of activating the coupling arrangement and of providing the operating medium for cooling the coupling. Admittedly, as a general rule, a significantly higher level of hydraulic pressure is required for the hydraulic activation of a transmission, especially an automatic transmission, than for the activation of the coupling. It has, however, been shown that, on the basis of the proposed invention, it is possible to implement, at comparatively low cost, for an extremely wide range of vehicles, especially those characterized by especially high performance ratings and/or especially high rotational frequencies, three different flow rates, which are required for the operation of a hydraulic wet clutch coupling system and a hydraulic transmission. These three flow rates specifically include: a high pressure at a relatively low flow rate, for activation of the coupling arrangement; a high pressure, or a very high pressure at a relatively low flow rate, for activation of the transmission; and a low pressure, at a relatively high flow rate, for cooling the coupling arrangement.

[0006] The controllable and/or adjustable pump can preferably be controlled or adjusted through the use of a pressure medium by means of a dedicated actuator, whereby the pressure medium for the control and/or regulation of the pump can preferably be provided on the basis of the pump arrangement and/or the pump itself.

[0007] A control circuit can preferably be provided, for the purpose of adjusting the output pressure and/or the output flow rate of the shared pump arrangement as a function of need, in order to reduce the energy consumption required by the pump arrangement. It is also conceivable to control the output pressure and/or the output flow rate as a function of need.

[0008] It is advantageously possible to provide a first pressure accumulator arrangement, which is allocated to the activation of the coupling, and a second pressure accumulator arrangement, which is allocated to the activation of the transmission, within a hydraulic system which is allocated to the drive train. As a further development in this connection, it is proposed that, in a first condition of the hydraulic system, the first pressure accumulator arrangement can be filled by means of the pump arrangement, and, in a second condition of the hydraulic system, the second pressure accumulator arrangement can be filled by means of the pump arrangement, and, in a further condition of a hydraulic system, the operating medium can be conducted to the coupling device at a maximal flow rate.

[0009] With regard to the controllable and/or adjustable pump, various types of pumps are conceivable—for example, an adjustable-eccentricity vane pump, or also adjustable axial or radial piston pumps.

[0010] The invention is described in greater detail below, by means of the designs set forth in the drawings attached hereto.

[0011]FIG. 1 shows, by way of example, a schematic representation of a basic structure of a coupling system according to the invention, with a wet clutch double coupling, whereby the transmission which is part of a vehicle drive train to which the coupling system belongs also appears in schematic representation.

[0012]FIG. 2 shows a concrete design of a coupling system according to the invention, according to the basic structure set forth in FIG. 1.

[0013]FIG. 1 shows, in schematic representation, a coupling system 200, which exhibits a wet clutch double coupling 202, with a first, radially outer coupling arrangement 206 and a second, radially inner coupling arrangement 204. Coupling arrangements 204 and 206 are wet clutch coupling arrangements—for example, wet clutch multiple disk clutch coupling arrangements—each of which, in a manner known from prior art, exhibits at least one set of disks, which, in the present design, are radially arranged one on top of the other, and each of which is activated by a dedicated activation piston of a hydraulic slave cylinder integrated into the double coupling. Examples of such double couplings are set forth in DE 100 04 179 A1.

[0014] The coupling system 200 exhibits a pump 209, which is mechanically driven by the drive unit—generally a combustion engine—of the drive chain. Preferably, the pump 209 is a hydrostatic pump or an extruder pump. The pump 209, which can be controlled and/or adjusted independently of the rotational frequency of the drive unit at any given moment, provides, by means of a distribution arrangement 230, a pressure medium, especially pressure oil, at a relatively high pressure, which is sufficient for the activation of the coupling arrangements 204 and 206 of the double coupling 202. For the alternative activation of the coupling arrangement, each of the coupling arrangements—or, more precisely, each of their hydraulic slave cylinders—is connected by means of a dedicated valve, 214 and 216 respectively, to the distribution arrangement 230 and thereby to the pump 209. The pump draws in pressure medium from a reservoir 222.

[0015] In addition, the pump provides, by means of the distribution arrangement 230, a relatively high flow rate of a cooling medium, especially cooling oil, at a—relatively—lower pressure level; said cooling medium serves to cool the coupling arrangements 204 and 206. In addition, the pump 209 provides, by means of the distribution arrangement 230, a pressure medium, especially pressure oil, at a relatively high or very high pressure level, which is sufficient for the activation of the transmission 232 of the drive train by means of a dedicated actuator 234. The transmission is preferably a double coupling transmission or a power shift transmission, which can be activated in an automated manner by means of a control unit (not shown). The transmission exhibits a first transmission input shaft which is dedicated to the first coupling arrangement 206 and a second transmission input shaft which is dedicated to the second coupling arrangement 204; said input shafts are preferably arranged coaxially to each other, with one transmission input shaft running through the other.

[0016]FIG. 2 shows, in greater detail, an design of a coupling system, according to the basic structure shown in FIG. 1.

[0017] According to FIG. 2, the cooling oil of the double coupling 202 (each of the two coupling arrangements whereof, 204 and 206, is represented in FIG. 2 by its own hydraulic slave cylinder, 424 and 426 respectively) is conducted by means of a heat exchanger 300, because, for example, in the case of a prolonged slippage operation, the temperature of the oil in the oil sump 222 can increase markedly. By means of the heat exchanger 300, the oil temperature is kept at a level which is sufficient to cool the double coupling. Because the cooling oil can become extremely viscous at lower temperatures and, on the basis of the flow resistance of the heat exchanger 300, it could happen that, at especially low temperatures, not enough cooling oil would reach the double coupling and/or too high an oil pressure could result in damage, a bypass valve 302—which, for example, is controllable by electrical means or, as an alternative, is spring-loaded—is provided. The bypass valve 302 opens or shifts into an opening position when the oil pressure downstream of the oil cooler 300 exceeds a predetermined pressure threshold, thereby letting the cooling oil in the oil cooler 300 through to the double coupling.

[0018] The pump 209, which is operated by the combustion engine 236 of the drive train, and which, for example, is configured so as to provide an output pressure of up to 120 bar, draws the oil from the reservoir 222 via a suction filter 322. Connected to the pump, on the output side, is another filter, known as a pressure filter 324, which is similarly provided with a bypass valve. A pressure sensor 326 serves to monitor the output pressure and, for the sake of safety, is provided with a pressure limit valve 328, which, should the pressure rise higher than, for example, 120 bar, opens and discharges pressure oil into the reservoir 222.

[0019] A coupling activation-pressure oil circuit is connected, by means of a relay valve 330, to the output side of the pump 209. The relay valve 330 is in turn connected to a clapper valve 332. Built into the coupling activation-pressure oil circuit is a pressure accumulator 304, which is kept under pressure and which exhibits a gas cushion. The pressure accumulator 304 is designed, for example, for a maximum pressure of 30 bar. The pressure accumulator 304 ensures a uniform pressure level and bridges the times in which the connection between the coupling activation-pressure oil circuit and the pump 209 by means of the relay valve 330.

[0020] Each of the activation slave cylinders of the two coupling devices 204 and 206 is connected to the pressure accumulator 304 by means of its own control/adjustment valve 214 and 216 respectively. The pressure oil circuit between the clapper valve 332 and the valves 214 and 216 is secured, by means of the pressure limit valve 308, against excessive pressure of the pressure oil which might lead to damage. The pressure limit valve 308 opens, for example, when a pressure of 30 bar is reached. The pressure determined in this pressure oil circuit by the fullness of the accumulator 304 is recorded by a pressure sensor 310.

[0021] An additional pressure limit valve 312 ensures that the pressure from valves 214 and 216, which operates on the hydraulic slave cylinders of the coupling devices, does not exceed a maximum value—for example, in order to avoid damage. Two clapper valves, 314 and 316, ensure that a single pressure limit valve is sufficient to monitor the activation pressure of both hydraulic slave cylinders and to protect the slave cylinders against overpressure.

[0022] The valves 214 and 216, which are preferably configured as pressure control/adjustment valves, adjust and/or control the pressure in the slave cylinders 424 and 426 that are allocated to both of the coupling arrangements of the double coupling 202. In the present design, what takes place is adjustment of the activation pressure of these slave cylinders. For this purpose, the output side of each of the valves 214 and 216 is provided with a pressure sensor, 428 and 430 respectively. Pulse dampers 432 and 434 prevent pressure peaks, thus enabling a reliable adjustment of the nominal pressure.

[0023] If we assume that the coupling arrangements are of the NORMALLY OPEN type, it will be advantageous to provide an emergency discharge valve 436 which, when triggered, allows pressure oil to flow into the reservoir 222. By allowing the discharge of pressure oil, the emergency discharge valve enables an emergency opening (or a fast opening) of whichever coupling arrangement is stressed in the direction of its engagement.

[0024] The cooling oil circuit, which is intended to supply the coupling arrangements with cooling oil, is connected to the output side of the pump 209 by means of an electrically switchable butterfly valve 440. In a first switching position, the flow of cooling oil, basically unchecked, is let through the butterfly valve 440, by way of the cooler 300 and/or the bypass 302, to the coupling device 202. In a second switching position of the butterfly valve 440, a throttle of the butterfly valve is activated, so as to let through only a rather low minimum flow rate of cooling oil to the coupling device and thereby to enable an increase of the oil pressure in the area between the pump 209, the butterfly valve 440 and the relay valve 330. In this way, when the relay valve 330 is open, the pressure accumulator 304 can be filled by way of the clapper valve 332. If the nominal pressure (maximum filling of the pressure accumulator 304) is reached (this can be determined, by way of the pressure sensor, by a dedicated electronic control unit), the relay valve 330 closes again, and, when necessary, the setting of the butterfly valve 440 changes from the throttle setting to the position which again allows the oil to flow through basically unchecked.

[0025] According to FIG. 2, an additional pressure accumulator 444 is connected to the pump 209 by way of a clapper valve 442. This pressure accumulator 444, which is configured for a higher pressure than the accumulator 304—for example, for a maximum pressure of 120 bar—serves to provide an actuator, which is dedicated to the transmission of the drive train, with pressure medium. This is shown in the illustrations in FIG. 1. This pressure accumulator 444, in a manner similar to pressure accumulator 304, can be filled in phases with less need of cooling. To this end, the butterfly valve 440 is brought into the throttle position and the relay valve is left closed. If the pump is then operated at full power, an increase in pressure takes place between the butterfly about 440, the relay valve 330 and the transmission actuator, until pressure values are reached which are sufficient to fill the accumulator 444. As a general rule, simultaneous filling of accumulator 304 and accumulator 444 is not possible because the maximum pressure of the accumulator 304 is not sufficient to enable the filling of the accumulator 444, which is configured for higher pressure values.

[0026] As set forth above, the output flow rate and/or the output pressure of the pump can be regulated (controlled and/or adjusted). Preferably, the pump is integrated into a control chain or—advantageously—a control circuit, in order to control or adjust the output flow rate and/or the output pressure as a function of need. In principle, the regulation of the pump can take place in any desired way —for example, by means of an electromechanical device (an electrical motor). However, it is preferable for the regulation of the pump to take place by means of pressure medium. This is provided in the design shown in FIG. 2. A hydraulic slave cylinder 450 is connected, by means of a control/adjustment valve 452, to the pressure accumulator 304. Through suitable control of the valve 452 by means of a dedicated control unit, the pump can be regulated as a function of need—possibly on the basis of characteristic diagrams. It would also be possible to adjust the pump on the basis of the output pressure recorded by the pressure sensor 326, relative to a predetermined nominal pressure value, which, in turn, could depend on the operational status.

[0027] Advantageously, a single control unit would be used to activate and/or control the various valves. The control unit would receive measurement signals from the various sensors—for example, also from at least one temperature sensor 454, which records the temperature of the oil in the reservoir 222.

[0028] A significant aspect of the design according to FIG. 2 is that only one pump which is driven by a combustion engine—that is, the pump 209—is provided, in order to handle the flow rate and pressure requirements. The pressure accumulator 304, which is provided in the coupling activation circuit, and the pressure accumulator 444, which is provided in the transmission activating circuit, ensure that the pump does not need to constantly provide the high supply volume at high pressure, because the accumulators are filled during the times when there is no need, or only a slight need, for cooling oil. To this end, as set forth above, valves 440 and 330 are switched in such a way that the oil supplied by the pump 209 will “pile up” to a certain extent, thus raising the pressure to the point where accumulators 304 and/or 444 can be filled. 

1. Drive train for a motor vehicle, which includes a coupling device (202) between a drive unit (232) and a transmission for moment transfer between the drive unit and the transmission, whereby the coupling device shows at least one coupling arrangement (204, 206) which can be activated by means of a pressure medium, for operation under the influence of an operating medium, and the transmission can be activated through the use of a pressure medium by means of a dedicated actuator (234), whereby, on the basis of a shared pump arrangement (209) that is or can be driven by the drive unit, i) the pressure medium can be provided for activation of the coupling arrangement, and ii) the operating medium can be conducted to the coupling device for the purpose of operating under the influence of the operating medium, and iii) the pressure medium can be provided for activation of the transmission, and whereby the pump arrangement includes at least one pump (209), which can be controlled or adjusted with regard to output pressure and/or with regard to output flow rate.
 2. Drive train according to claim 1, wherein the pump (209) can be controlled or adjusted by means of a dedicated actuator (452, 450), through the use of pressure medium, whereby the pressure medium for control and/or adjustment of the pump can preferably be provided on the basis of the pump arrangement (209).
 3. Drive train according to claim 1 or 2, wherein said drive train includes a control circuit for the purpose of adjusting the output pressure and/or the output flow rate of the pump arrangement (209) as a function of need.
 4. Drive train according to any of claims 1 to 3, wherein a first pressure accumulator arrangement (304), which is allocated to the activation of the coupling, and a second pressure accumulator arrangement (444), which is allocated to the activation of the transmission, are provided within a hydraulic system.
 5. Drive train according to any of the previous claims, wherein the coupling arrangement (204, 206) is a wet clutch coupling arrangement, wherein the operation taking place under the influence of the operating medium is a wet clutch operation, and wherein the operating medium is an operating fluid, such as a cooling fluid.
 6. Drive train according to any of the previous claims, wherein the coupling device is configured as a multiple coupling device, especially a double coupling device (202), and exhibits a first coupling arrangement (206), to which at least one first slave cylinder (424) is dedicated, and a second coupling arrangement (204), to which at least one second slave cylinder (426) is dedicated, whereby the medium provided by the pump arrangement (209) as a pressure medium can be conducted to both of the slave cylinders independently of each other.
 7. Coupling system for a drive train according to any of the previous claims, which exhibits: at least one coupling arrangement (204, 206) that can be activated by means of a pressure medium, for operation under the influence of an operating medium, and a shared pump arrangement (209) that is or can be driven by a drive unit of the drive train, on the basis of which i) the pressure medium can be provided for activation of the coupling arrangement, and ii) the operating medium can be conducted to the coupling device for the purpose of operating under the influence of the operating medium, and iii) the pressure medium can be provided for activation of a transmission (232) which can be activated by means of pressure medium, and whereby the pump arrangement includes at least one pump (209), which can be controlled or adjusted with regard to output pressure and/or with regard to output flow rate. 